Add the ability for extensions to provide language settings (#10296)

This PR adds the ability for extensions to provide certain language
settings via the language `config.toml`.

These settings are then merged in with the rest of the settings when the
language is loaded from the extension.

The language settings that are available are:

- `tab_size`
- `hard_tabs`
- `soft_wrap`

Additionally, for bundled languages we moved these settings out of the
`settings/default.json` and into their respective `config.toml`s .

For languages currently provided by extensions, we are leaving the
values in the `settings/default.json` temporarily until all released
versions of Zed are able to load these settings from the extension.

---

Along the way we ended up refactoring the `Settings::load` method
slightly, introducing a new `SettingsSources` struct to better convey
where the settings are being loaded from.

This makes it easier to load settings from specific locations/sets of
locations in an explicit way.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/language/src/language_settings.rs

@@ -10,7 +10,7 @@ use schemars::{
     JsonSchema,
 };
 use serde::{Deserialize, Serialize};
-use settings::{Settings, SettingsLocation};
+use settings::{Settings, SettingsLocation, SettingsSources};
 use std::{num::NonZeroU32, path::Path, sync::Arc};
 
 impl<'a> Into<SettingsLocation<'a>> for &'a dyn File {
@@ -119,7 +119,7 @@ pub struct CopilotSettings {
 }
 
 /// The settings for all languages.
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema)]
 pub struct AllLanguageSettingsContent {
     /// The settings for enabling/disabling features.
     #[serde(default)]
@@ -140,7 +140,7 @@ pub struct AllLanguageSettingsContent {
 }
 
 /// The settings for a particular language.
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Default, PartialEq, Serialize, Deserialize, JsonSchema)]
 pub struct LanguageSettingsContent {
     /// How many columns a tab should occupy.
     ///
@@ -249,7 +249,7 @@ pub struct LanguageSettingsContent {
 }
 
 /// The contents of the GitHub Copilot settings.
-#[derive(Clone, Debug, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, Debug, PartialEq, Default, Serialize, Deserialize, JsonSchema)]
 pub struct CopilotSettingsContent {
     /// A list of globs representing files that Copilot should be disabled for.
     #[serde(default)]
@@ -257,7 +257,7 @@ pub struct CopilotSettingsContent {
 }
 
 /// The settings for enabling/disabling features.
-#[derive(Clone, Default, Serialize, Deserialize, JsonSchema)]
+#[derive(Clone, PartialEq, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(rename_all = "snake_case")]
 pub struct FeaturesContent {
     /// Whether the GitHub Copilot feature is enabled.
@@ -473,11 +473,9 @@ impl settings::Settings for AllLanguageSettings {
 
     type FileContent = AllLanguageSettingsContent;
 
-    fn load(
-        default_value: &Self::FileContent,
-        user_settings: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self> {
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
+        let default_value = sources.default;
+
         // A default is provided for all settings.
         let mut defaults: LanguageSettings =
             serde_json::from_value(serde_json::to_value(&default_value.defaults)?)?;
@@ -500,7 +498,8 @@ impl settings::Settings for AllLanguageSettings {
             .and_then(|c| c.disabled_globs.as_ref())
             .ok_or_else(Self::missing_default)?;
 
-        for user_settings in user_settings {
+        let mut file_types: HashMap<Arc<str>, Vec<String>> = HashMap::default();
+        for user_settings in sources.customizations() {
             if let Some(copilot) = user_settings.features.as_ref().and_then(|f| f.copilot) {
                 copilot_enabled = copilot;
             }
@@ -528,11 +527,8 @@ impl settings::Settings for AllLanguageSettings {
                     user_language_settings,
                 );
             }
-        }
 
-        let mut file_types: HashMap<Arc<str>, Vec<String>> = HashMap::default();
-        for user_file_types in user_settings.iter().map(|s| &s.file_types) {
-            for (language, suffixes) in user_file_types {
+            for (language, suffixes) in &user_settings.file_types {
                 file_types
                     .entry(language.clone())
                     .or_default()